The present invention is directed to disc drive heads. Specifically, the present invention is directed to configurations of disc drive readers that reduce the amount of sensed off-track magnetic flux.
Disc drives have read and write heads that convert magnetic field lines stored on the disc into electrical signals that are processed to produce computer usable data. The discs have data tracks that are positioned as concentric circles. The read and write heads are positioned over a track by an actuator arm that is driven by a servomechanism. The track contains magnetic field lines whose orientation varies throughout the track. The disc is rotated and the magnetic field lines pass under the read/write head. Magnetic flux emanates from the disc and is sensed by the head.
Data is sequentially read from a track as the disc rotates. Adjacent data tracks rotate by the read head as the current data track rotates directly beneath the head""s sensing element. Magnetic flux lines also emanate from adjacent tracks. If the read element in the head is not sufficiently shielded from the adjacent tracks"" magnetic flux, the electrical signals generated by the read element may not correctly correspond to the magnetic flux of the current data track. In such a case, the data that results from processing the electrical signal will be invalid. Similarly, when writing data, if the flux emanating from the write head is not contained to the current data track, data contained in the adjacent tracks may become invalid. As the track density increases to provide greater amounts of storage per unit area, the degree of shielding necessary for proper reading and writing of the data must also be increased.
Typically, the read and write portions are joined and have three pole pieces to help shield the read and write processes. A giant magnetoresistive head, known as a spin valve configuration, is shown in FIG. 2 as an example. The pole pieces, 202, 208, and 204, are positioned sequentially. The middle or shared pole piece 208 is shared between the read and write processes. In the write process, the magnetic flux extends from the top pole piece 202 to the shared middle pole piece 208. In the read process, the magnetic flux extends from the bottom pole piece 204 across the gap 206 and through the read element 210 to the shared middle pole piece 208. The magnetic flux originates from magnetic medium 212 that forms the surface of the disc.
Several read elements are available for disc drives. Magnetoresistive (MR) films are one type and are used in the spin valve configuration of FIG. 2. MR elements have an electrical resistance that is directly related to their magnetic orientation (i.e. the direction of a magnetization vector). When an MR element 210 is exposed to magnetic flux, the magnetic orientation of the MR element changes (i.e. the magnetization vector points in a different direction creating an angle between the rest direction and the resulting vector direction), and its electrical resistance is thereby altered. To read the data, MR elements are driven with a constant electric current and a voltage drop across the element changes as the resistance changes in response to the element being exposed to the magnetic flux. The voltage drop is measured and processed to generate the data values sent to the computer system from the disc drive.
As with all read elements, MR elements must be shielded to prevent reading magnetic flux from tracks adjacent to the current data track. FIG. 2-2 shows an air bearing slider (ABS) view of the spin valve configuration shown in FIG. 2. An ABS view is one taken upwardly from the surface of the recording medium into the bottom of the slider. In the prior art, as shown in FIG. 2-2 which is the ABS view taken along line 2-2 of FIG. 2, the two pole pieces 208 and 204 that shield the MR element 210 provide a gap, or separation zone that the MR element 210 resides between. In the spin valve configuration of FIGS. 2 and 2-2, the separation distance is increased at the ends of the pole pieces that lie above the adjacent tracks. The separation distance must be increased to permit electrical connectors 214, 216 and stabilizing magnets 218, 220 to be placed to the sides of the read element 210. These electrical connectors and stabilizing magnets have been omitted from FIG. 2.
In the spin valve configuration, the electrical connectors 214 and 216 are used to supply the biasing current to the GMR (giant magnetoresistive) element and are positioned in the separation zone adjacent to the GMR element. The stabilizing magnets 218 and 220, also positioned within the separation zone adjacent to the GMR element, are used to create a single domain state. The single domain state occurs when the magnetization vectors are consistent throughout the GMR element. The single domain state provides a more accurate voltage drop due to the magnetic flux from the recording medium. Spin valves utilize about 4 sensor layers in the read element with each layer being about 10-50 xc3x85 thick. The sensor layers are made of magnetic material and usually 2 layers are placed together to form a pair. Thus the read element contains 2 pairs, and these are separated from one another by a non-magnetic material that conducts electrical current such as copper.
The GMR element""s magnetic orientation vectors are important because flux from the recording medium must increase the voltage drop to represent one binary state or decrease the voltage drop to represent the other binary state. Maintaining the angle between the two vectors at 90 degrees is necessary for proper interpretation of the data state because the angle is related to the voltage by a cosine function. If the angle is too close to 0 degrees, then a change in the angle will always result in the voltage increasing. If the angle is too close to 180 degrees, then a change in the angle will always result in the voltage decreasing. In either case, distinguishing a one from a zero is not possible.
The GMR element will have an inherent magnetic orientation vector on each side of the conductor running through the element when no bias current is applied. The films are made so the vector on one side parallel to the vector on the other side, and the vectors typically are parallel with the longitudinal direction of the element. One magnetic film is permanently oriented by a pinning layer that causes the resulting magnetic orientation vectors to create the necessary angle of 90 degrees relative to one another.
Similar to the spin valve, an anisotropic MR configuration uses a single sensor layer in the read element that is about 100-200 xc3x85 thick to produce a usable voltage drop. Anisotropic configurations also utilize side conductors to provide the bias current and stabilizing magnets to create the single domain state. Spin valves produce a greater voltage drop for the same amount of flux from the recording medium than do anisotropic MR configurations. However, some potentially troublesome flux from adjacent tracks will be channeled into the read element by the wider separation zones over the adjacent data tracks in both of these configurations. This stray magnetic flux will interfere with the magnetic flux from the current track and may cause invalid data to result.
Rather than using standard anisotropic magnetoresistive heads or spin valve configurations where the biasing current flows through the length of the read element in a direction parallel to the plane of the recording medium as shown in FIGS. 2 and 2-2, some read heads employ vertical giant magnetoresistive (VGMR) read heads. In vertical giant magnetoresistive heads, the current flows perpendicular to the horizontal plane of the recording medium. Thus, electrical conductors are not needed on the sides of the read element that lie over the adjacent data tracks. Instead, conductors are placed above and in some cases below the read element. The stabilizing magnets are not necessary because MR elements used in the vertical configuration can now be manufactured to inherently maintain a single domain state with vectors at 0 degrees when no biasing current is applied. This single domain state is created by techniques well known in the art such as combining shape anisotropy and magnetocrystalline anisotropy. Alternatively, nearby layers of antiferromagnetic or ferromagnetic layers may be added. However, the read element in the vertical configuration is still susceptible to receiving flux emanating from tracks adjacent to the current data track.
A disc drive""s read/write head would benefit from shielding configurations that avoid channeling flux from adjacent tracks to the read element. Avoiding the flux from the adjacent tracks ensures the integrity of the data that is being read and enables greater storage per unit area of disc space.
Accordingly, the present invention is found in a disc drive read head which reduces off-track magnetic pickup by the read element. The embodiments of the present invention are found in a method for configuring the head to avoid the stray magnetic flux. A read element is placed in a first zone formed by the separation between two magnetic pole pieces forming a read gap that shield the read element from the stray magnetic flux. In operation, the read element is positioned over a current data track. A second zone is formed by the separation between the two magnetic pole pieces forming the read gap and in operation is positioned over data tracks that are adjacent to the current data track.
A first separation width is provided for the space between the two magnetic pole pieces for the first separation zone. The first width is great enough to permit the read element to be placed in the first separation zone. In some embodiments, the read element is partially surrounded by a gap and is electrically connected to one of the pole pieces. In others, the read element is completely surrounded by a gap within the first separation zone. The width of this zone is determined by usual considerations of bit resolution and flying height to achieve the necessary read back pulse widths.
A second separation width is provided for the space between the two magnetic pole pieces for the second separation zone. The second separation width is less than the first separation width and may be as small as zero (i.e. the shields may be connected). The lesser width of the second separation zone prevents stray magnetic flux from the adjacent data tracks from reaching the read element.
The present invention may also be found in an apparatus configured to reduce the off-track pick-up. The apparatus is a read/write head that includes the two pole pieces forming the read gap and the read element. The first and second pole pieces are separated in the two zones. The first separation zone has a greater width for the space between the pole pieces and overlays the current data track when installed in the disc drive. The second zone is for placement over data tracks adjacent to a current data track and has the narrower separation for the space between the pole pieces, which prevents the stray flux from reaching the read element. The read element resides within the first zone and senses the flux from the current data track.
Another embodiment of the present invention is found in a read head that reduces the amount of sensed stray magnetic flux. The read head contains a read element that is placed over a current data track in operation of the disc drive. A means for enclosing the read head is provided to reduce the amount of magnetic flux that emanates from tracks adjacent to the current data track and that is sensed by the read element.
These and other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.